The present invention relates to hammer drills, and more particularly, to a hammer drill capable of achieving high blows per minute relative to the output shaft speed.
When drilling through hard surfaces such as rocks or stone, many times it is desirable to impart a reciprocating motion to the drill bit to facilitate drilling. This hammering motion of the drill bit helps break up the material while the rotating of the drill bit allows the broken up material to be removed from the hole being drilled.
A conventional hammer drill has a motor disposed in a housing, and the motor includes an armature shaft having a pinion at its end. The pinion drives a suitably arranged set of gears to rotate the output shaft. A drill chuck is mounted on the output spindle to receive a drill bit.
In conventional designs, the impact mechanism which provides the hammering action is typically associated with the face of an output gear connected to the output shaft. More specifically, a ratchet face or similar mechanism on the face of the output gear abuts a cooperating mechanism that is affixed to the drill housing. A reciprocating motion is then imparted to the drill bit when the output shaft rotates.
It is also well known in the art to provide hammer drills with the capability to switch between a conventional drilling mode, with rotation only, and a hammer drilling mode employing conventional drill rotation along with a hammer action. The hammer drill is capable of switching between the two modes, and thus eliminates the need for a separate conventional drill. An example of an adjustment mechanism for switching between conventional drilling mode and hammer drilling mode is disclosed in U.S. Pat. No. 5,447,205 assigned to the assignee of the present invention which is incorporated herein by reference.
A primary disadvantage associated with existing impact mechanisms for hammer drills is the fact that in order to accomplish a desired high blows per minute (BPM) for efficient hammer drill performance, an undesirable high output speed is required. High BPM can also be achieved by increasing the number of ramps on the impact mechanism. However, an increased number of impact ramps tends to produce a xe2x80x9cskippingxe2x80x9d effect and efficiency loss due to the smaller area of surface contact for each ramp.
One solution which achieves both high BPMs without a corresponding need to increase output speed is disclosed in commonly owned U.S. Pat. No. 5,653,572, and which is also incorporated herein by reference. More specifically, an intermediate gear of a two stage gear reduction arrangement is made axially displaceable and associated with a first cam mechanism for generating a reciprocating (i.e., hammer) motion. An output face is engageable with an impact face of an output gear. Engagement of the output and impact faces transmits axial displacement between the intermediate and output gears. A second cam mechanism is affixed to the housing and axially spaced from the first cam mechanism. The first and second cam mechanisms are engageable by sufficiently axially displacing the output shaft so that the output gear impact face abuts the intermediate gear output face while the first and second cam mechanisms abut each other. The first and second cam mechanisms are configured to generate reciprocating motion and cause the intermediate gear to reciprocate axially as the first cam mechanism rotates relative to the second cam mechanism, which is then transmitted to the impact face of the output gear to axially reciprocating the output shaft as it rotates.
While this arrangement satisfactorily divorces the relationship between the output shaft speed and the BPMs of the hammer action, the use of high speed motors in some drill applications, such as the high speed motors typically employed in cordless drills, requires very high reduction in speed between the drive shaft of the motor and the output shaft which rotates the chuck. A two stage gear reduction arrangement may not be suitable for such high gear reduction applications. As such, a need still exists for a hammer drill hammer mechanism which produces high BPMs without a concomitant increase in output shaft speed while also providing the ability to achieve a high gear reduction.
In addition, it is known to include a spindle locking arrangement in industrial hammer drills to prevent rotation of the output shaft while allowing the hammering action to take place. Such arrangements advantageously allow a hammer drill to operate in a third hammer only or xe2x80x9cchippingxe2x80x9d mode.
For example, U.S. Pat. No. 5,415,240 (Mundjar) discloses a hammer drill employing a percussion piston/striking bar hammer arrangement driven by a rotary fluid valve. Switching between a hammer, hammer/drill, and drill mode is achieved by axial movement of a pinion gear attached to the motor shaft. U.S. Pat. No. 3,955,628 (Grxc3x6zinger et al) discloses a hammer drill which can be selectively switched between a hammer, hammer/drill, and drill mode by use of a cam to axially displace the output shaft to cause engagement of a hammer disk with an impact member, and a coupling member into engagement with stationary cutout. In U.S. Pat. No. 3,789,933 (Jarecki), a hammer drill is disclosed which can be selectively switched between a hammer, hammer/drill, and drill mode by use of a coupler and an axially moveable external locking collar. This arrangement acts directly on the output shaft to control rotation thereof. Finally, U.S. Pat. No. 4,236,588 (Mxc3x6ldan et al) and U.S. Pat. No. 4,763,733 (Neumaier) both provide hammer drills which utilize separate rotary and hammer drive mechanisms. Both arrangements also use an axially displaceable coupling sleeve to switch between rotation of the output shaft and rotation locking. Mxc3x6ldan ""588 also discloses an intermediate mode wherein the output shaft is freely rotatable but not engaged.
While such arrangements provide hammer drills capable of operating in a hammer only mode of operation, either independent hammer and rotation drive systems are employed which undesirably increase the size, weight, and cost of the drill, or complex mechanical spindle locking arrangements are used when the hammer and rotation motions are driven by a single motor. In addition, such common drive arrangements all suffer from the inability to achieve a high BPMs without a corresponding increase in output speed, as described above.
Thus, a need exists for a hammer drill capable of operating in a third hammer only mode which utilizes a simple spindle locking arrangement, while also allowing a high BPM without a corresponding increase in output shaft speed.
It is, therefore, an object of the present invention to provide a hammer drill capable of generating a high blows per minute (BPM) without requiring an undesirable high output speed in combination with a high reduction gearing arrangement.
It is another object of the present invention to provide a hammer drill capable of generating a high blows per minute (BPM) without requiring an undesirable high output speed which further includes a simple spindle locking arrangement to allow the hammer drill to operate in a hammer only chipping mode.
In accordance with these and other objects and features of the present invention, a hammer drill is provided with an impact mechanism for generating a reciprocating action on an output shaft. A chuck is attached to the end of the output shaft for attachment of various types of tool bits. The hammer drill includes a motor for driving an intermediate gear stage. The intermediate gear stage includes an axially displaceable gear element arranged therein to form a spindle locking mechanism which permits selective control of whether the output shaft is driven in either a reciprocating motion only setting, or a combined rotational and reciprocating motion setting. In addition, a mechanism is provided to selectively disengage the output shaft from interacting with the impact mechanism to allow driving of the output shaft in a rotational motion only setting.
In accordance with one embodiment of the present invention, a hammer drill capable of operation in a hammer drill mode, a drill-only mode, and a chipping mode is provided having a housing, a motor disposed in the housing and having a rotatable armature shaft and an armature pinion located at one end thereof, and an axially displaceable output shaft having an outer end adapted to receive a drill chuck. An output gear is fixed about the output shaft to rotate coaxially therewith, and an intermediate gear reduction arrangement is provided having at least a first gear engageable with the armature pinion, an axially displaceable second gear engageable to drive the output gear, and a rotation control mechanism for selectively moving the second gear into and out of driving engagement with the output gear. An axially displaceable first cam mechanism is positioned to be driven by the armature shaft, and a second cam mechanism is affixed to the housing. The first and second cam mechanisms are arranged to be engageable by selectively displacing the first cam mechanism to cause the first and second cam mechanisms to abut each other, wherein the first and second cam mechanisms are configured with respect to each other and the intermediate gear reduction arrangement to generate reciprocating motion in response to rotation of the armature shaft and cause the intermediate gear reduction arrangement to transmit the reciprocating motion to the output gear thereby axially reciprocating the output shaft irrespective of whether the second gear and the output gear are in rotational engagement.
In accordance with another embodiment of the present invention, the intermediate gear reduction arrangement includes a first planetary gear set having a sun gear driven by the armature pinion gear and an outer gear for driving the sun gear of a second planetary gear set. The second planetary gear set includes a sun gear and an outer gear for driving the output gear to cause the output shaft to rotate. In accordance with a further aspect of this embodiment, the sun gear of the second planetary gear set can form the axially displaceable second gear if a chipping mode is desired, such that rotation of the output shaft can be prevented by selectively moving the axially displaceable sun gear out of engagement with the outer gear of the second planetary gear set. In this embodiment, the first impact cam mechanism is located on the armature pinion.
In accordance with a further embodiment of the present invention, the intermediate gear reduction arrangement includes a two stage gear reduction arrangement having a first intermediate shaft to which the second gear is affixed. If a chipping mode is desired, the first intermediate shaft can be arranged to be axially displaceable to move the second gear out of engagement with the output gear to prevent rotation of the output shaft. In this embodiment, the first cam mechanism is located on the armature shaft.
In still another embodiment of the present invention, the intermediate gear reduction arrangement comprises a three stage gear reduction arrangement having a second intermediate shaft to which to which the second gear is affixed. If chipping mode is desired, the second intermediate shaft is axially displaceable to move the second gear out of engagement with the output gear to prevent rotation of the output shaft. The three stage gear reduction arrangement farther comprises a first intermediate shaft to which the first gear is affixed. The first cam mechanism is located on the first gear, and the first intermediate shaft is axially displaceable to move the first and second cam mechanisms into and out of engagement.
The advantages accruing to the present invention are numerous. For example, the present invention allows a desired high blows per minute (BPM) for efficient hammer drill performance without a concomitant high output shaft speed or costly two-speed gear train to be used with high speed motors such as employed in cordless dill applications. In addition, the use of a simple spindle locking mechanism allows the hammer drill to be used in a chipping or chiseling mode.